Rigid conduit systems include a plurality of joints to which the ends of the rigid conduits are attached. The joints, in themselves, may be rigid, but in many applications it is desired that the system have a degree of flexibility, and in those cases the joint includes flexing structure capable of accommodating angular adjustment between adjacent conduits of a limited degree without leakage or loss of integrity of the conduit system. Flexible joints for a rigid conduit system must be capable of withstanding tension and compression axial forces imposed upon the conduits, i.e. "end loads" as well as restrain torsional loads, and must also remain leak prook even though misalignment between adjacent conduits has occurred.
One type of joint that has been used by the assignee to interconnect the ends of adjacent rigid conduits is a joint utilizing a double gimbal mechanical interconnection. In this type of double gimbal joint a gimbal ring includes four pivot pin members mounted upon the ring at 90.degree. intervals about the circumference thereof. An annular collar is connected to the end of the conduits, such as by solder or welding, and extensions of the collar pivotally cooperate with two pivot pins on the ring which are in diametrically opposed relation. In this matter the adjacent ends of the conduits attached to a common joint are capable of pivoting about axes related 90.degree. to each other, and in a common plane, wherein a universal angular displacement between the conduits in all directions is possible, and the joint effectively prevents relative axial displacement between the adjacent conduits under end loads.
The collars affixed to a common joint are sealed with respect to each other by a short flexible conduit, such as a metal bellows, which will permit limited angular displacement between adjacent conduits while maintaining the fluid tight integrity of the system. As the gimbal joint absorbs all of the axial forces imposed upon the conduits the flexible conduit need not have a high strength resistance to axial forces, and need only be capable of withstanding the internal fluid pressures.
In the double gimbal joint constructions previously available, including those produced by the assignee, the gimbal ring assembly consists of a circular ring of a substantially solid machined construction having four pivot pins in the form of rivets circumferentially radially extending through the ring at 90.degree. intervals. The collars are pivotally attached to the rivets at the exterior of the ring, and accordingly, a bending or "single" shear stress is placed upon the pivot pin rivets by end loads imposed upon the conduits. Such forces imposed upon the pivot rivets may cause rivet failures which can result in excessive deformation and forces being applied to the flexible conduit interconnecting the joint collars, resulting in leakage and failure of the conduit system.
It is an object of the invention to provide a gimbal joint for rigid conduit or duct systems wherein a gimbal ring assembly is formed of sheet metal, and wherein an improved distribution of shear forces upon pivot structure is attained.
Another object of the invention is to provide a double gimbal joint for rigid conduit systems wherein all of the components, other than the pivot pin structure, may be formed of sheet metal without sacrifice of stress resistant characteristics.
An additional object of the invention is to provide a double gimbal joint for use with rigid conduit systems utilizing a gimbal ring formed of inner and outer sheet metal rings maintained in spaced relationship wherein pivotal connections upon the ring assembly occur intermediate the spaced rings.
Yet another object of the invention is to provide a double gimbal joint for rigid conduit systems wherein collars of the joint are interconnected by a flexible metallic conduit and the joint includes a protective shield extending over portions of the flexible conduit.
In the practice of the invention the joint consists of a pair of annular collars mounted upon opposite sides of a double gimbal ring assembly wherein the collars are pivotally connected to the ring assembly for pivotal movement about axes perpendicularly related to each other within a common plane. The double gimbal ring assembly is formed by a cylindrical inner sheet metal ring circumscribed by an outer sheet metal ring having a convex transverse cross section. The inner and outer rings are maintained in a radially spaced relationship by four pivot pin assemblies located at 90.degree. intervals about the circumferences of the inner and outer rings.
The pivot pin assemblies each include an annular spacer having a circular periphery located between the inner and outer rings to maintain the radial spacing therebetween, and a pivot pin rivet extends through each spacer, and through aligned holes defined in the inner and outer rings to assemble the spacers to the rings and maintain the assembly of the gimbal ring.
The annular collars are located upon opposite axial sides of the gimbal ring assembly and each include a cylindrical surface to which the rigid conduits are sealingly affixed by welding, soldering, or other bonding techniques. Each collar is mounted to the gimbal ring by a pair of sheet metal fork lugs welded or soldered to the associated collar, and the fork lugs of a common collar extend intermediate the inner and outer gimbal assembly rings and are pivotally associated with spacers located at diametrically opposed locations on the ring assembly. The fork lugs engage the cylindrical surfaces of the spacer means, and in this manner the collars, and associated conduits, are capable of universal adjustment relative to each other due to the 90.degree. orientation of the pivot axes of the collars.
The collars are sealed with respect to each other by a flexible metal conduit having a serpentine wall similar to a bellows. Each end of the flexible conduit is sealed to collar structure, and the flexible conduit encompasses the double gimbal ring assembly. Each collar includes a protective metal skirt which extends over a portion of the flexible conduit, less than half the axial dimension thereof, and these skirts aid in protecting the flexible conduit against external damage.
The portion of the fork lugs located intermediate the ring assembly inner and outer rings is of a convex configuration corresponding to the configuration of the outer ring, and preferably, a sheet metal reinforcing element is spot welded to the underside of the fork lugs at the location of engagement with the spacer to reinforce the fork lug at its pivot location. As the rivet extends through the inner and outer rings, and is thereby supported upon the rings upon opposite sides of the spacer, and as the fork lugs engage the spacer intermediate the inner and outer rings, a "double" shear relationship is established between the fork lugs and the rivets providing superior shear resistance as compared to prior art double gimbal joints using a solid ring assembly construction wherein a "single" shear relationship exists between the fork lugs and rivets.
The aforedescribed description of the double gimbal conduit joint results in an economically producible joint having excellent load resisting characteristics against end loads and torsion forces within the conduit system, yet the joint permits ready pivoting between adjacent conduits to accommodate adjustment, misalignment or assembly requirements. The separate fabrication of the fork lugs with respect to the collar simplifies manufacturing without sacrificing operating characteristics, and the protective skirts for the flexible conduit interconnecting the collars minimizes the likelihood of damage to the flexible conduit without adversely affecting the gimbal action of the joint.